A type of endoprosthesis device, commonly referred to as a stent, may be placed or implanted within a vein, artery or other tubular body organ for treating occlusions, stenoses, or aneurysms of a vessel by reinforcing the wall of the vessel or by expanding the vessel. Stents have been used to treat dissections in blood vessel walls caused by balloon angioplasty of the coronary arteries as well as peripheral arteries and to improve angioplasty results by preventing elastic recoil and remodeling of the vessel wall. Two randomized multicenter trials have recently shown a lower restenosis rate in stent treated coronary arteries compared with balloon angioplasty alone (Serruys, P W et. al. New England Journal of Medicine 331: 489-495, 1994, Fischman, D L et. al. New England Journal of Medicine 331: 496-501, 1994). Stents have been successfully implanted in the urinary tract, the bile duct, the esophagus and the tracheo-bronchial tree to reinforce those body organs, as well as implanted into the neurovascular, peripheral vascular, coronary, cardiac, and renal systems, among others. The term "stent" as used in this application is a device which is intraluminally implanted within bodily vessels to reinforce collapsing, dissected, partially occluded, weakened, diseased or abnormally dilated or small segments of a vessel wall.
One of the drawbacks of conventional stents is that they are generally produced in a straight tubular configuration. The use of such stents to treat diseased vessels at or near a bifurcation (branch point) of a vessel may create a risk of compromising the degree of patency of the primary vessel and/or its branches, or the bifurcation point and also limits the ability to insert a second stent into the side branch if the result of treatment of the primary, or main, vessel is suboptimal. Suboptimal results may occur as a result of several mechanisms, such as displacing diseased tissue, plaque shifting, vessel spasm, dissection with or without intimal flaps, thrombosis, and embolism.
The risk of branch compromise is increased generally in two anatomical situations. First, a side branch may be compromised when there is a stenosis in the origin of the side branch. Second, when there is an eccentric lesion at the bifurcation site, asymmetric expansion can cause either plaque shifting or dissection at the side branch origin. There are reports of attempts to solve this problem by inserting a balloon into the side branch through the struts of a stent deployed in the main branch spanning the bifurcation point; however, this technique carries the risk of balloon entrapment and other major complications (Nakamura, S. et al., Catheterization and Cardiovascular Diagnosis 34: 353-361 (1995)). Moreover, adequate dilation of the side branch is limited by elastic recoil of the origin of the side branch. In addition, insertion of a traditional stent into a main vessel spanning a the bifurcation point may pose a limitation to blood flow and access to the side branch vessel. The term "stent jail" is often used to describe this concept. In this regard, the tubular slotted hinged design of the Palmaz-Schatz intracoronary stent, in particular, is felt to be unfavorable for lesions with a large side branch and is generally believed to pose a higher risk of side branch vessel entrapment where the stent prevents or limits access to the side branch. Id.
One common procedure for intraluminally implanting a stent is to first open the relevant region of the vessel with a balloon catheter and then place the stent in a position that bridges the treated portion of the vessel in order to prevent elastic recoil and restenosis of that segment. The angioplasty of the bifurcation lesion has traditionally been performed using the "kissing" balloon technique where two guidewires and two balloons are inserted, one into the main branch and the other into the side branch. Stent placement in this situation requires the removal of the guidewire from the side branch and reinsertion through the stent struts, followed by the insertion of a balloon through the struts of the stent along the guidewire. The first removal of the guidewire poses the risk of occlusion of the side branch during the deployment of the stent in the main branch.
Prior art patents refer to the construction and design of both the stent as well as the apparatus for positioning the stent within the vessel. One representative patent to Chaudhury, U.S. Pat. No. 4,140,126, discloses a technique for positioning an elongated cylindrical stent at a region of an aneurysm to avoid catastrophic failure of the blood vessel wall. The '126 patent discloses a cylinder that expands to its implanted configuration after insertion with the aid of a catheter. Dotter, U.S. Pat. No. 4,503,569, discloses a spring stent which expands to an implanted configuration with a change in temperature. The spring stent is implanted in a coiled orientation and is then heated to cause the spring to expand. Palmaz, U.S. Pat. No. 4,733,665, discloses a number of stent configurations for implantation with the aid of a catheter. The catheter includes a mechanism for mounting and retaining a stent, preferably on an inflatable portion of the catheter. The stents are implanted while imaged on a monitor. Once the stent is properly positioned, the catheter is expanded and the stent separated from the catheter body. The catheter can then be withdrawn from the subject, leaving the stent in place within the blood vessel. Palmaz, U.S. Pat. No. 4,739,762, discloses an expandable intraluminal graft. Schjeldahl et. al., U.S. Pat. No. 4,413,989, discloses a variety of balloon catheter constructions. Maginot, U.S. Pat. No. 5,456,712 and Maginot, U.S. Pat No. 5,304,220 disclose a graft and stent assembly and a method of implantation where a stent is used to reinforce a graft that is surgically inserted into a blood vessel in order to bypass an occlusion. However, none of these patents relate to stents which are structurally adapted for the treatment of bifurcation lesions, or disclose a bifurcating stent apparatus.
Taheri , U.S. Pat. No. 4,872,874, Piplani et. al., U.S. Pat. No. 5,489,295, and Marin et al., U.S. Pat. No. 5,507,769, disclose bifurcating graft material which may be implanted using stents as anchors for the graft. However, bifurcated stents are not taught or disclosed, and the purpose of the stent as used in these inventions is simply to anchor the graft into the vessel wall. It does not reinforce the vessel wall, treat a lesion, or prevent restenosis after angioplasty.
MacGregor, U.S. Pat. No. 4,994,071, discloses a hinged bifurcating stent. In the 071' patent, in contrast to the present invention, there is a main stent with two additional stents attached at one end of the main stent, creating a single unit with a trunk attached at an end to two smaller stents. The two additional stents are permanently attached to the end of the trunk (and not the side, as in the present invention) and cannot be removed from the main stent. Thus, this invention may not be used to treat only one branch of a bifurcated vessel, is not appropriate for use when the branch vessel extends laterally from the side of a main vessel (as opposed to an end of a main vessel), and does not cover the origin of a bifurcated vessel or bifurcation lesion. In addition, studies with hinge-containing stents have shown that there is a high incidence of restenosis (tissue growth) at the hinge point that may cause narrowing or total occlusion of the vessel and thus compromise blood flow. Furthermore, this design has a relatively large size as compared to the present invention, which makes insertion into many smaller vessels difficult and poses a greatly increased risk of complications. Also, by having the two additional smaller stents connected to an end of the trunk stent, tracking into a wide-angle lateral side branch may be difficult and may carry the risk of dissection of the vessel wall. Furthermore, once the device of the '071 patent is implanted, it is impossible to exchange a branch stent should the need for a different stent size or repair of a branch stent arise.
Marcade, U.S. Pat. No. 5,676,696, discloses a bifurcated graft assembly used for repairing abdominal aortic aneurysms, comprising a series of interlocked tubes, one of which comprises a fixed angle single bifurcated graft assembly. In contrast to the present invention, Marcade discloses a graft, not a stent, which may not be used to treat only one vessel of a bifurcation (leaving the untreated vessel free from all obstructions). In addition, and in contrast to the present invention, the one-piece bifurcated graft portion of Marcade is uniform in size and fixed in angle, and may not be used in a vessel bifurcation where the branch and the main vessels differ greatly in size. Also, the fixed angle will not provide as exact a fit as the variably-angled branched double-stent of the invention.
U.S. Pat. No. 5,653,743 to Martin discloses a bifurcated graft assembly for use in the hypogastric and iliac arteries. In addition to teaching grafts (which are used to replace diseased vessel material) and not stents (which, as used herein, reinforce existing vessels) Martin, in contrast to the present invention, discloses a side branch graft attached to the main graft as a single unit, requiring a larger profile than the subject stent. Martin also claims and discloses much larger component sizes and methods for implantation (appropriate for the hypograstric artery, to which Martin is limited) than are operable in smaller vessels, such as those of the cardiac, coronary, renal, peripheral vascular, gastrointestinal, pulmonary, urinary or neurovascular system, or brain vessels. In addition, Martin requires two vascular access sites (FIG. 3, elements 16 and 18), whereas the device of the present invention requires only one access site, creating less trauma to the patient.
U.S. Pat. No. 5,643,340 to Nunokowa discloses a synthetic vascular bypass graft in which a side branch graft extends outward from the side of a second portion of the graft unit. Nunokawa, however, discloses surgically implanted extraluminal grafts and not intraluminal stents deployed by catheterization, and is therefore unrelated to the subject of bifurcation lesions and stents, particularly stents used to intraluminally reinforce bifurcated vessels. In contrast to the present invention, Nunokawa is surgically implanted outside of the lumen of a vessel and in fact is used to bypass damaged regions of a vessel entirely. The present invention is used to reinforce the diseased region, and is intraluminally implanted directly into the diseased region. Additionally, and unlike the present invention, the Nunokawa device is surgically implanted and after surgical assembly of its components forms a single permanently attached unit, wherein the bifurcating stent devices of the invention are deployed intraluminally by catheter and do not require surgery or the suturing or attaching of parts of the invention to each other or to the body vessels, allowing for adaptation to varying branch vessel angles. Also, unlike the present invention, Nunokawa does not require visualization by x-ray or ultrasound, as the Nunokawa device is directly seen during surgery. Lastly, the Nunokawa device cannot be deployed using catheters, is not inserted intraluminally in a compressed state and expanded while inside a vessel, and has a much larger profile than the present invention.
In general, when treating a bifurcation lesion using commercially available stents, it is important to cover the origin of the branch because if left uncovered, this area is prone to restenosis. In order to cover the branch origin, conventional stents inserted into the branch must protrude into the lumen of the main artery or vessel from the branch (which may cause thrombosis, again compromising blood flow). Another frequent complication experienced when stenting bifurcated vessels is the narrowing or occlusion of the origin of a side branch spanned by a stent placed in the main branch. Additionally, placement of a stent into a main vessel where the stent partially or completely extends across the opening of a branch makes future access into such branch vessels difficult if not impossible. As a result, conventional stents are often placed into the branch close to the origin, but generally not covering the origin of the bifurcation.
Lastly, conventional stents are difficult to visualize during and after deployment, and in general are not readily imaged by using low-cost and easy methods such as x-ray or ultrasound imaging. While some prior art balloon catheters (and not stents) are "marked" at the proximal and distal ends of the balloon with imageable patches, few stents are currently available which are marked with, or which are at least partly constructed of, a material which is imageable by currently known imaging procedures commonly used when inserting the stents into a vessel, such as ultrasound or x-ray imaging. The invention described in this Application would not work with endoscopy as currently used as an imaging method due to size limitations, but future advances in limiting the size of endoscopic imaging devices may in the future make endoscopic imaging compatible with the stents of the invention.
Accordingly, there is a need for improved stent apparatuses, most particularly for applications within the cardiac, coronary, renal, peripheral vascular, gastrointestinal, pulmonary, urinary and neurovascular systems and the brain which 1) completely covers the bifurcation point of bifurcation vessels; 2) may be used to treat lesions in one branch of a bifurcation while preserving access to the other branch for future treatment; 3) allows for differential sizing of the stents in a bifurcated stent apparatus even after the main stent is implanted; 4) may be delivered intraluminally by catheter; 5) may be used to treat bifurcation lesions in a bifurcated vessel where the branch vessel extends from the side of the main vessel; and 6) is marked with, or at least partly constructed of, material which is imageable by commonly used intraluminal catheterization visualization techniques including but not limited to ultrasound or x-ray.